Radikalische Polymerisation mit Silyl-Radikalen. Photopolymerisation von Styrol mit Bis(trimethylsilyl)-quecksilber

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The baeyer-villiger reaction of strained cage compounds, 1,3-bishomocubanones,via carbocations

The Baeyer-Villiger oxidation of 1,3-bishomocubanone 1a in chloroform with m-chloroperbenzoic acid (m-CPBA) at room temperature proceeds quite rapidly and gives the ordinary lactone, 10-oxapentacy-clo[5.4.0.0^2.5.0^3.9.0^4.8]undecan-11-one 2a and the skeletal rearrangement product, 11-oxapentacy-clo[6.3.0.0^2.4.0^3.7.0^5.9]undecan-10-one 4a. Methyl substituted homologs (1d, 1e, 1f) of 1a give the corresponding ordinary and rearranged lactones (2d, 2e, 2f, 4d, 4e, 4f). In these oxidations, the mechanism via carbocations, cyclobutyl 18 and cyclopropylcarbinyl cations 19, plays a major role different from the ordinary concerted migration mechanism. Solvent effects, kinetic treatments, and methyl substituent effects on product ratios support this carbocation mechanism. The adduct formation process between a ketone and m-CPBA must be rate-determining.     

Palladium-catalyzed direct arylation of thiazoles with aryl bromides

Thiazole, 2-phenyl or -alkyl substituted one and benzothiazole are efficiently arylated with aryl bromides at the 2- and/or 5-position(s) in the presence of Pd(OAc)₂ and a bulky phosphine ligand using Cs₂CO₃ as base. 2-Phenyl-5-thiazolecarboxanilide undergoes successive diarylation at the 4- and 5-positions accompanied by decarbamoylation.     

Surface phonon anomalies in superconducting transition metal compounds

The surface phonon dispersion curves of superconducting refractory materials are shown to present important anomalies induced by the electron-phonon interaction, similar to those appearing in the bulk phonon dispersion. A Green function calculation of surface dynamics for TiN(001), based on a cluster-deformability model, predicts anomalies in the Rayleigh wave, as well as in the surface quasi-longitudinal acoustic and optical branches. The Rayleigh wave anomaly turns out to be shifted down to one half of the zone with respect to the bulk anomaly occurring at $\text{2}\text{3}$ of the zone. Such shift is directly related to the surface-induced change in the average range of electron-phonon interaction. Recent He scattering data on NbSe₂(0001) are commented on in the light of the present theoretical prediction.     

Polymere, die stabile freie Radikale enthalten. 4. Mitt. Darstellung von 2,4-Diphenyl-6-(3-maleoyliminophenyl)-3,4-dihydro-s-tetrazin-1(2H)-yl und dessen anionische Polymerisation

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Stable barium compounds in YBa2Cu3Oy superconductors

The stability of various amounts of Ba₃Cu₃In₄O₁₂ (334) or BaTbO₃ (BTO) in a sintered YBa₂Cu₃O_y (YBCO) matrix was examined. Samples with added 334 or BTO exhibited critical temperatures (T_c) above 90 K for up to 20 vol.% addition and improved critical current densities (J_c) under a magnetic field. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis indicated that 334 and BTO did not react with the YBCO matrix under the sintering conditions used. The normalized J_c under a magnetic field of 1 T reached a maximum at 14 vol.% of 334 addition and 20 vol.% BTO addition. YBCO thin films with added BTO showed a gradual decrease in the T_c with increasing BTO content. YBCO films with added 334 showed a constant T_c of 87 K up to a 334 content of 4 vol.%.     

Stickelberger ideals and Fitting ideals of class groups for abelian number fields

In this paper, we determine completely the initial Fitting ideal of the minus part of the ideal class group of an abelian number field over Q up to the 2-component. This answers an open question of Mazur and Wiles (Invent Math 76:179–330, 1984) up to the 2-component, and proves Conjecture 0.1 in Kurihara (J Reine Angew Math 561:39–86, 2003). We also study Brumer’s conjecture and prove a stronger version for a CM-field, assuming certain conditions, in particular on the Galois group.     

Nature of electron transport by pyridine-based tripodal anchors: potential for robust and conductive single-molecule junctions with gold electrodes

We have designed and synthesized a pyridine-based tripodal anchor unit to construct a single-molecule junction with a gold electrode. The advantage of tripodal anchoring to a gold surface was unambiguously demonstrated by cyclic voltammetry measurements. X-ray photoelectron spectroscopy measurements indicated that the π orbital of pyridine contributes to the physical adsorption of the tripodal anchor unit to the gold surface. The conductance of a single-molecule junction that consists of the tripodal anchor and diphenyl acetylene was measured by modified scanning tunneling microscope techniques and successfully determined to be 5 ± 1 × 10(-4)G(0). Finally, by analyzing the transport mechanism based on ab initio calculations, the participation of the π orbital of the anchor moieties was predicted. The tripodal structure is expected to form a robust junction, and pyridine is predicted to achieve π-channel electric transport.